In that case, Sigurd SHOULD have appeared in Brawl, even if he had only one appearance, he is a LOT more IMPORTANT than Ike, and popular (Celice can beat that though) in Japan. But no, Marth (old) and Ike (new) were in Brawl. Because Old and new casts are shown in Brawl (Lucario = Perfect EXAMPLE).
And FE6 a failure? Wow, coming from a modern Fire Emblem fan, no surprise. You don't know a thing of Japan, FE6 is the Third Best-Selling FE Game, while FE9 had really low sales in Japan. (Pfft, before you say something about world-widely, i'd not say anything about it if I were you).
Let's put this on the case, FE7 had a sequel (well, technically, FE6) and how did the fans reacted? simple:
They wanted FE6 to be brought to the entire world. The Elibe legacy would have gotten Roy back as a rep. in Brawl if his game would had been launched later for the entire world, but it wasn't. (This comes in response to your FE9 to FE10 thing).
FE9 being a very recieved game by fans is simple: is a Gamecube game, and in world-wide logic: Gamecube Games > Game Boy Advance Games. Simple logic, really simple. If Eliwood and Co. had their game in the GCN... you can now think of it, heh. Ike is just popular because he is a character from a Gamecube FE game.
FE9 and FE10 did not do anything overly special anyways, just brought back the Skills that were already present in FE4. If any series did anything special for Intelligent Systems, it is FE4 (try to deny that, oh wait... you can't).
However, this doesn't means Ike is not a good character, of course, he is because he got all this, bravo. He can still be kicked out of SSB4 if forgotten, but I doubt it, highly doubt it.
Edit: Oh, I forgot to reply your points stated before... but those are plain ridiculous, be more-in-depht in the Fire Emblem world, please, and you'll see that some of those points are not real.
